Surface Roughening in Formed Al Sheets for Automative Applications. Final Report

New experimental and analytical tools for characterizing various types of forming-induced surface roughening have been developed and used to study the evolution of surface roughening in 6000 series aluminum sheets in the T4 condition. Particular attention was focused on the evolution of the ''diamond defect,'' which often requires a subsequent mechanical surface treatment to achieve an acceptable surface finish. Testing was primarily done in plane strain tension and samples evaluated at various strain levels up to and including the forming limit. Characterization techniques included optical and scanning electron microscopy, white light phase shift interferometry, and orientation imaging microscopy. Roughening patterns were observed to communicate through the sheet thickness, e.g., peaks on one side correspond to peaks on the other; valleys to valleys. At the grain or grain cluster scale, roughening was found to be governed by the Schmid rather than the Taylor factor